中文摘要：

采用ReaxFF反应分子动力学方法研究了不同压缩态β-HMX晶体（ρ=1.89、2.11、2.22、2.46、2.80、3.20 g·cm-3）在T=2500 K时的热分解机理, 分析了压力对初级和次级化学反应速率的影响、高压与低压下初始分解机理的区别以及造成反应机理发生变化的原因. 发现HMX的初始分解机理与压力（或密度）相关. 低压下（ρ〈2.80 g·cm-3）以分子内反应为主, 即N－NO2键的断裂、HONO的生成以及分子主环的断裂（C－N键的断裂）. 高压下（ρ≥2.80 g·cm-3）分子内反应被显著地抑制, 而分子间反应得到促进, 生成了较多的O2、HO等小分子和大分子团簇. 初始分解机理随压力的变化导致不同密度下的反应速率和势能也有所不同. 本文在原子水平对高压下HMX反应机理的深入研究对于认识含能材料在极端条件下的起爆、化学反应的发展以及爆轰等具有重要意义.

英文摘要：

The thermal decomposition mechanisms of condensed phase β-HMX at various densities （ρ= 1.89, 2.11, 2.22, 2.46, 2.80, 3.20 g·cm-3） and at 2500 K were studied using ReaxFF reactive molecular dynamics simulations. The effects of pressure on the initial and secondary reaction rates, the main differences in the initial decomposition mechanisms between highly compressed and less compressed systems, as well as the reasons for these variations were analyzed. It was determined that the initial decomposition mechanisms of HMX were dependent on pressure （or density）. At low densities （ρ〈2.80 g· cm-3）, intramolecular reactions are dominant, these being N-NO2 bond dissociation, HONO elimination, and concerted ring fission by C-N bond scission. At high densities （ρ ≥2.80 g·cm-3）, intramolecular reactions are well restrained, whereas intermolecular reactions are promoted, leading to the formation of small molecules, such as O2 and HO, and large molecular clusters. These changes in the initial decomposition mechanisms lead to different kinetic and energetic behaviors, as well as variations in the distribution of products. These results obtained through this work are significant in that they assist in understanding the chemical reactions involved in the initiation, reaction development, and detonation of energetic materials under extreme conditions.